The calibration of the camera is a one time process but it is also one of the most important processes to get the highest accuracy from Dragonfly. It allows to create a calibration file that encodes the distortion parameters of the camera optics. These distortion parameters are a function of the manual assembly process of the camera optics and of any enclosure used to protect the camera. The calibration file is used by Dragonfly to “normalize” the wide-angle images collected by the camera.

1 – Preliminary steps

1. Launch Dragonfly and connect your monocular camera (following the information of the left menu).
2. Click on the Three lines button and then on the Calibrate camera button.
3. Type the calibration File name using a meaningful name (e.g. 180_Low_Illumination_Camera)
4. Download the following calibration pattern: CHESSBOARD grid
5. Print the calibration pattern on a A4 or Letter paper with no margin and place it on a plain surface.
   • Do not perform the calibration if the calibration pattern printed is wavy because you won’t be able to perform a good calibration and Dragonfly won’t produce accurate results!
6. Width – leave it to 640
7. Height – leave it to 480
8. Measure the distance in millimeters (NO inches and NO centimeters!) of the HDIST line visible inside the calibration pattern.
9. Enter the distance just measured inside the field H DIST.
10. Select the Mode that you would like to use for the calibration process.
    • free auto mode – allows to perform the calibration process by pointing a calibration pattern from the angles chosen by the users. The poses used for the calibration will be AUTOMATICALLY collected by Dragonfly every 1 second.
    • free mode – allows to perform the calibration process by pointing a calibration pattern from the angles chosen by the users. The poses used for the calibration will be collected by Dragonfly after having clicked on a button of the GU
11. Inside the Pattern select the calibration pattern chose: chessboard.
12. Inside the Dist model field choose:
    • Wide Fov – if you are working with a 170° camera.
    • Fisheye 4 distortion coeff – if you are working with a 180° camera.

2 – Calibration steps

2.1 – Free-auto mode

The free auto mode allows to perform the calibration process by pointing a calibration pattern from the angles chosen by the users. The poses used for the calibration will be AUTOMATICALLY collected by Dragonfly every 1 second.

1. Click on Start calibration.
2. Now you just have to point the camera towards the calibration pattern until you should see the black dots/squares being connected by colored lines. The first pose will be AUTOMATICALLY captured by Dragonfly (and you will see the taken image count counter growing).
   • Please make sure that the camera and the pattern are close. Otherwise the calibration result won’t be usable!
3. Now you have to move the camera and point the calibration pattern from a different angle every 1 second so that Dragonfly can capture all the other poses.
4. You will have to collect a total of 21 poses. Please make sure to collect images close to the pattern and from different angles!
5. After you have collected all the poses, the Dragonfly App will automatically start the computation of the calibration parameters of your camera.
   • It should take few seconds and the calibration file will be automatically saved inside the configuration folder of the Dragonfly App.
   • If you see a black screen instead of the video feed coming from your camera, then there are chances that the calibration process did not produce a good calibration file. In this case you just have to repeat the calibration process.
6. Then the calibration file is automatically saved and the state will be: CALIBRATED.
7. Click on the Return button to exit the calibration process.

2.2 – Free mode

The free mode allows to perform the calibration process by pointing a calibration pattern from the angles chosen by the users. The poses used for the calibration will be collected by Dragonfly after having clicked on a button of the GUI.

1. Click on Start calibration.
2. Now you just have to point the camera towards the calibration pattern until you should see the black dots/squares being connected by colored lines. When this happens click on the camera button to capture the pose and you will see the taken image count counter growing.
   • Please make sure that the camera and the pattern are close. Otherwise the calibration result won’t be usable! 
3. Now you can move the camera and point the calibration pattern from another angle.
4. You will have to collect a total of 21 poses. Please make sure to collect images close to the pattern and from different angles!
5. After you have collected all the poses, the Dragonfly App will automatically start the computation of the calibration parameters of your camera.
   • It should take few seconds and the calibration file will be automatically saved inside the configuration folder of the Dragonfly App.
   • If you see a black screen instead of the video feed coming from your camera, then there are chances that the calibration process did not produce a good calibration file. In this case you just have to repeat the calibration process.
6. Then the calibration file is automatically saved and the state will be: CALIBRATED.
7. Click on the Return button to exit the calibration process.

Now, we recommend to check the calibration quality by following the next steps.

3 – Verify the calibration quality

To verify the calibration quality please:

1. Click on the Three lines button and then on the Site settings button.
2. Click on the Camera menu and chose the Camera sub-menu.
3. Select the Calibration File just computed and click on Preview
4. Now point the camera towards a square or rectangular shape and verify that the lines/shapes that are straight on the square/rectangular shape are also straight inside the video preview.
   • If this is the case then the calibration computed is good.
   • If this is NOT the case then it might be that something went wrong during the calibration process. Please repeat the calibration process and make sure to
     • Select:
       • Wide Fov – if you are working with a 170° camera.
       • Fisheye 4 distortion coeff – if you are working with a 180° camera.
     • Collect images close to the pattern and from different angles!

4 – Convert the calibration file with the resolution used for your project

The calibration file just computed works when Dragonfly is used at 640 x 480 resolution. If you need to use Dragonfly at a different resolution please get in touch with Onit at support.onplant@onit.it and we will convert your calibration file so that you can use it at 720 x 960 or 1080 x 1440.